1. Field of the Invention
This invention relates generally to a valve including pressure equalization and, more particularly, to a shut-off valve for a compressed hydrogen tank, where the valve includes two inlet ports that provide pressure equalization so that the valve can be opened with reduced force at high inlet pressures.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cell systems as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
A hydrogen fuel cell is an electrochemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free hydrogen protons and electrons. The hydrogen protons pass through the electrolyte to the cathode. The hydrogen protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle.
Many fuel cells are typically combined in a fuel cell stack to generate the desired power. For example, a typical fuel cell stack for a vehicle may have two hundred or more stacked fuel cells. The fuel cell stack receives a cathode input gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen in the air is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen input gas that flows into the anode side of the stack.
In some vehicle fuel cell systems, hydrogen is stored in one or more compressed gas tanks under high pressure on the vehicle to provide the hydrogen necessary for the fuel cell system. The pressure in the tank can be upwards of 700 bar. In one known design, the compressed gas tank may include an inner plastic liner that provides a gas tight seal for the hydrogen, and an outer carbon fiber composite layer that provides the structural integrity of the tank. Because hydrogen is a very light and diffusive gas, the inner liner must be carefully engineered in order to act as a permeation barrier. The hydrogen is removed from the tank through a pipe. At least one pressure regulator is provided that reduces the pressure of the hydrogen within the tank to a pressure suitable for the fuel cell system.
Further, a shut-off valve is required either in the tank or just outside of the tank that closes the tank when the fuel cell system is off. A stiff spring is typically used to maintain the valve in the closed position and prevent hydrogen leaks. Because the pressure in the compressed hydrogen tank may be very high, the pressure difference between the inlet side and the outlet side of the shut-off valve may be very large. Therefore, the force required to open the valve against the pressure difference and the spring bias is significant. Electromagnets are sometimes used in these types of shut-off valves to open the valve. However, electromagnets are generally not the most desirable valve choice because of the amount of energy required to open the valve, and the size and weight of the electromagnet.